Should you create 1 article for each long tail KW?

If there's 1000 long tail KWs, that's a lot of articles, especially if they need to 2k+ words long.

Well, 1000 long tail keywords? I didn't get this point, but making a full article for each long tail keyword isn't always a good idea because most cases they looks like each other and you will get "Keyword Cannibalization" in the end.
Like:

Best Gaming Monitor Under 300
Best Gaming Monitor Under 200
Best Gaming Monitor Under 100

If you did a 3 articles for all keywords, mostly "not always" you will have Best Gaming Monitor Under 200 ranking instead of "Best Gaming Monitor Under 300"
and they will mix up in the 3 queries, so it's better to make "Best Budget Gaming Monitor" and start listing the "Best Gaming Monitor Under 300/200/100" in the same article, and having different anchor texts in the backlinks for the 3 phrases so you rank for the 3 phrases etc..

Ideally you should focus on 1 main keyword per article. However it's possible to target multiple keywords in one article. With higher site authority you'll find it easier to rank multiple keywords.

So you could setup your main article like this

Best Toaster

-Best toaster under 200
--Best black toaster under 200
-best 4 slice toaster

etc. etc. That way you can target all the long tail variants of best toaster in one article if you want to. As long as they are closely related then yeah put them in the same article. The longer article will help with ranking anyway as google will give you bonus points. Longer articles also usually mean lower bounce rates which is an important ranking factor (when combined with other behavioural factors)

No, you don't want 1,000 articles targeting very similar keywords. We are way beyond one keyword - one article. Learn about RankBrain - it's about making 2K words long articles (or longer in most cases) targeting tens of keywords. Of course, you want to target LSI and long tail keywords alongside with your main keywords. Of course, you don't want to over-optimise your article either. Make sure that article read well and made for readers, not Google.

Already mentioned above how to use keywords which meaning similar. Ok. I want to add another important point. Keywords tools provide a lot of keywords variations and it's natural. You have to research and take some good knowledge about the niche.

So that you can understand what people are looking for, how they search, what they exactly want to know, how much details, variations, etc. When you know, you can decide topics. You can differentiate unique topics. And also understand how in-depth information you should cover for each unique topic.

This way you can understand how many possible pages can create for that niche. After that, you can select the main keyword (may target longtails) for each topic and rest others as their secondary keywords. So each longtail keywords should not be your unique topic/page.

You can target related keywords in 1000 articles, but not similar keywords, please. Also, you should focus on one long-tail keyword per article, then apply 1% keyword density. -Micah

I think if you plan 3000+ word article for a long tail key word is a good idea.
Huge content is always good for the website.
But keep one thing in your mind "keyword density"

You don't need to focus on each long-tail keyword. Write about your niche using important keywords and write naturally for the user, google's AI will pick up the topic and your keywords, it will compare it to other kw-s people are searching for to find your type of content, if your content matches it will rank. Tho I haven't been a fan of content marketing, personally I find good backlinks be more worth than writing content for google.